Iv M, Liu X, Lavezo J, et al. - Given a better correlation of fractional tumor burden with histologic tumor volume fraction in treated glioblastoma vs other perfusion metrics such as relative CBV (cerebral blood volume), researchers sought to define fractional tumor burden classes with low and high blood volume to distinguish tumor from treatment effect and to ascertain the value of fractional tumor burden in treatment-related decision-making. Following surgical sampling, they performed retrospectively evaluation of 47 patients with high-grade gliomas (primarily glioblastoma) with recurrent contrast-enhancing lesions on DSC-MR imaging. Treatment effect vs tumor was defined via histopathologic examination. In each histopathologically defined group, they used normalized relative CBV thresholds of 1.0 and 1.75 to define low, intermediate, and high fractional tumor burden classes. In this study, high fractional tumor burden defined fractions of the contrast-enhancing lesion volume with high blood volume whereas low fractional tumor burden defined fractions of the contrast-enhancing lesion volume with low blood volume, and these may assist in differentiating treatment effect from tumor in recurrent glioblastomas. Further, they identified fractional tumor burden maps as valuable to inform clinical decision-making.